Sculpting brushes behaves weird
You don't have enough resolution on your mesh to go with or you have bad setting of dyntopo that generates less resolution than before.

first things first, apply scale before sculpting by ctrl + A > scale

then we have many methods of sculpting in 2.79 including: sculpting with multires modifier, sculpting with Dyntopo

some of the ways you can use Dyntopo are using relative detail or constant detail.

when on relative detail, having a small number on it and zooming in gives you more detail.

when on constant detail having a larger number gives you more detail. one of the downsides of Dyntopo is that it can be heavy to work with so it's good to just use detail flood fill option and disable Dyntopo. note that Detail flood fill does not work on relative detail option of dyntopo.